1. Field of the Invention
The present invention relates to a simulation apparatus, a simulation method, and a computer program product for performing a simulation of a reaction phenomenon in a semiconductor process.
2. Description of the Related Art
With a semiconductor process apparatus using a chemical vapor deposition method, reactive ion etching, or the like, to analyze the phenomenon in the reaction chamber and perform a simulation using a computer is a technique that is essential to the achievement of process control at a high level. Thus, in a manufacturing process of a semiconductor product, which requires extremely a fine processing, the process needs to be controlled with a high degree of precision, and the simulation needs to be performed with a high degree of precision.
In a reaction chamber in a process apparatus, various phenomena are intricately involved with one another, including the transport of heat and fluids, a plasma physical phenomenon caused by electron excitation, influences from external electric fields and magnetic fields, and chemical reactions caused by ion bombardments and thermal energy. Thus, although today's computer environment is advanced, it takes a long time and also it is not easy to calculate these phenomena accurately.
Further, the chemical reactions on the wall surfaces of the reaction chamber and on the surface of the semiconductor substrate sometimes have a strong influence, as boundary conditions, on the phenomena occurring in the reaction chamber. Also, the magnitude of the influence of the reactions occurring on the surface of the semiconductor substrate exerted on a vapor phase phenomenon in the reaction chamber depends on not only numerical values, which can be defined using chemical reaction expressions, but also factors related to the microstructure including the material of which the surface is made.
For example, let us discuss a situation in which a chemical reaction vapor deposition method utilizing thermal energy (i.e. a thermal Chemical Vapor Deposition (CVD) method) is used, and the supplied source gases have a decomposition reaction on the surface of a semiconductor substrate and is deposited. In this situation, the reactivity of the source gases are often low. For example, statistically speaking, there is a possibility that, of 105 vapor phase molecules that collide against the surface of the semiconductor substrate, only one molecule actually has a reaction on the surface and is deposited as a film (the reaction probability is expressed as 10−5). In this situation, the deposition rate of the film on the surface of the substrate is substantially the same, regardless of whether the substrate surface is a smooth plane (i.e. a plane structure) or the substrate surface is a surface with an uneven profile (i.e. an uneven structure). For example, if an area having an uneven structure is ten times larger than an area having a plane structure, the consumption speed of the vapor phase molecules with the uneven structure is ten times larger than the consumption speed with the plane structure.
However, even if the surface profile is the same, when molecules that have a high reactivity and have the reaction probability of 1 form a deposition film, the deposition speed of the film at an internal portion of the uneven profile (i.e. the inner wall portion) is lower than the deposition speed on the plane (i.e. the upper surface portion). Consequently, the consumption speed of the vapor phase molecules is the same, regardless of whether the substrate has a plane structure or an uneven structure.
Also, in a Reactive Ion Etching (RIE) process to perform an etching process with high-speed ions that are highly anisotropic, the surface of a solid is etched by the ions, and the etching products are released as gas molecules. It is known that the released etching product molecules may be re-deposited on the surface. The amount of the re-deposited molecules has a strong influence on a processed-profile in the reactive ion etching process. For example, when an etching process is performed on a substrate over an etching mask that has a low reactivity with ions, and if the ion anglar distribution is very highly anisotropic, the ions collide against substantially the mask substance and cause no reaction. Thus, there is hardly any product generated in the etching process. However, when the ions are less anisotropic, many reactive ions collide against even the side-wall surfaces on which there is no mask. Accordingly, the side-wall surfaces are etched, and a lot of etching products are released.
As described above, in a semiconductor process apparatus, the phenomena occurring in the reaction chamber are strongly linked to the microstructure on the wall surface of the reaction chamber or on the semiconductor substrate. Thus, to perform a simulation with a high degree of precision, it is necessary to take into consideration the mutual interactions between the vapor phase and the surface.
However, although semiconductor process apparatuses have a size of some centimeters to meter order, the surface structure of a semiconductor substrate is often a microstructure from micrometers to nanometers. Thus, the mesh sizes used in the numerical value calculations to perform calculations efficiently are mutually different between the semiconductor apparatus and the surface structure. Thus, it is difficult to perform numerical simulations at the same time on the phenomena related to the semiconductor apparatus and the phenomena related to the surface structure. For this reason, in conventional semiconductor process simulations, the calculations are often performed by simply assuming that the surface of a semiconductor substrate is a plane surface, which means that the microstructure on the surface is ignored, or by only taking into consideration macro area-size ratios of a plurality of surfaces that are made of mutually different materials (Y. Akiyama et al., J. Crystal Growth 241 (2002) 352.).
In the simulation disclosed in Carlo Cavallotti et al., J. Crystal Growth 248 (2003) 411, a simulation 1 in which a calculation is performed for a process reaction chamber, using a relatively larger calculation mesh, and a simulation 2 in which a calculation is performed for a specific microstructure on the surface, using a very small calculation mesh are performed According to the method, it is proposed that convergence calculations are performed repeatedly so that, in a boundary region, the concentrations of the vapor phase reactive molecules and the concentration gradients become the same in the simulation 1 and the simulation 2.
Further, Japanese Patent Application Laid-open No. H8-106449 discloses a simulation method for an interactive reaction between a solid phase base and vapor phase particles being incident to the solid phase by which the attribute of a particle in the solid phase base is determined (e.g. an attribute of Si or an attribute of O) so that the behavior is determined according to the base particle to which a vapor phase particle has adhered.
However, a problem remains with the simulation method disclosed in Y. Akiyama et al., J. Crystal Growth 241 (2002) 352, where it is not possible to perform a simulation accurately, while a mutual interaction between the microstructure on the surface of the semiconductor substrate and the vapor phase is taken into consideration.
In addition, although the simulation method disclosed in Carlo Cavallotti et al., J. Crystal Growth 248 (2003) 411 is a physically accurate approach, a problem remains where it takes a long time to perform the calculation when complicated chemical reactions and plasma phenomena are dealt with.
Also, as for the simulation method disclosed in Japanese Patent Application Laid-open No. H8-106449, a problem remains where it is not possible to apply the method to an apparatus simulation for a semiconductor process apparatus that has a larger scale than the surface structure of the semiconductor substrate.